Suction systems of this kind generally comprise a container and a suction catheter connected to the container inlet, the outlet of the container being connected to a vacuum pump so that a reduced pressure is created in the container which in turn applies suction to the catheter. In such systems, the vacuum pump generally operates continuously and the catheter includes a valve by which suction at the tip of the catheter can be controlled. In its simplest form, the valve comprises an aperture in the wall of the catheter which, when open, allows air to enter the catheter and thereby prevents any significant suction effect at the tip. The aperture can be closed, when desired, by the thumb of the user, or by a movable flap, so that the suction effect is confined to the tip of the catheter. The valve is located close to the patient end of the catheter so that the surgeon can control the valve with the same hand as he uses to manipulate the tip of the catheter. Examples of such catheters are described in U.S. Pat. Nos. 3,911,919 and 4,468,216. The problem with this form of valve is that the suction control aperture provides a path through which contaminated material sucked into the catheter can leak out. This is a significant disadvantage in view of the present concern about cross-infection and the transmission of infectious diseases.
In order to reduce the risk of escape of material, catheters have been made which include a sealed valve. Examples of suction catheters with a push-down spool valve are shown in U.S. Pat. Nos. 4,680,026, 4,526,573 and 4,502,508. A suction catheter with a resilient valve member is described in U.S. Pat. No. 4,569,344. Many other forms of suction catheter with different suction control valves are also known.
One problem with these valves is that, because they must have a high integrity seal to prevent escape of suction fluid externally of the device and inadvertent suctioning of the patient, the cost of the valve forms a large part of the total cost of the system. This is a particular disadvantage in a product which is disposed of after use on one patient. Another problem is that there can be a risk of blockage in the valve, especially where the catheter is used for suctioning of fluid containing thick tenacious mucous, tissue debris or blood clots. Currently-available valves form an integral part of the suction system and are specified for 24 hour use on a single patient. The valves cannot be re-used because this would involve re-use of the system as a whole and the attendant risk of cross-infection.